1. Field of the Invention
This invention relates to measuring magnetoresistive (“MR”) head resistance and more particularly relates to measuring the MR head resistance using a constant reference current.
2. Description of Related Art
A magnetic data storage device such as a magnetic tape drive, hard disk drive, and the like often employs a MR head to record data to or read data from a magnetic media such a magnetic tape, a hard disk, and the like. The magnetic data storage device typically employs at least one MR head to read data and at least one head to write data.
A write head writes data to the magnetic media by creating a magnetic field in response to an electronic signal. The magnetic field varies in response to changes in the strength and polarity of the electronic signal. In addition, the varying magnetic field modifies the magnetic polarization of the magnetic media in a region of the magnetic media adjacent to the write head. Thus by encoding data as changes of strength and polarity in the electronic signal, the write head encodes the data as magnetic polarities on the magnetic media as the write head moves relative to the magnetic media.
A read MR head reads data from the magnetic media by creating an electronic signal as induced by the change of magnetic polarities between the various regions of the magnetic media as the read MR head moves relative to magnetic media. Because the data was written to the magnetic media as changes in magnetic polarity, the electronic signal from the read MR head may be decoded to retrieve the data from the magnetic media.
The performance of the MR head is highly sensitive to the electrical characteristics of the MR head. In particularly, a manufacturer must know the electrical resistance of the MR head. In the past, the resistance of the MR head has been measured by applying known reference current to the MR head, measuring a voltage across the MR head, and calculating the resistance from the reference current and the voltage. Unfortunately, the reference current used to measure the resistance is often not known with sufficient precision or accuracy, reducing the precision and accuracy of the calculated resistance.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that measure MR head resistance independent of any measurement of the reference current. Beneficially, such an apparatus, system, and method would more precisely and accurately measure the resistance of the MR head.